STOCKTON - Drivers on California roads on weekend nights are more likely to have drugs than alcohol in their systems, according to a results of a survey released by state officials on Monday.

About 14 percent of drivers surveyed tested positive for drugs that could impair their ability to drive, according to the California Office of Traffic Safety. That's nearly twice as many drivers as the 7.3 percent who tested positive for alcohol, according to the survey.

The survey was the first of its kind in the state, but safety officials said it reinforced what other statistics have shown is a growing problem.

"While the use of alcohol while driving has been lessening, drugged driving has been growing," said Chris Cochran, an Office of Traffic Safety spokesman. Quantifying the problem with the survey is a step toward fighting it, he said. "This is just another step in determining how best to combat drugged driving."

Unlike with alcohol, there is no defined legal limit for the drugs - both legal and illegal - that can impair driving. Officers across the state undergo special training to help them detect drug-impaired drivers, according to safety officials. These include officers in Stockton, at DUI checkpoints and on patrol, said Officer Joe Silva, a Stockton Police Department spokesman.

It starts with recognizing the symptoms of drug use, then testing if the driver is impaired. "(Officers) will run a series of tests ... to see if drivers are under the influence," he said.

Whether a driver is under the influence of drugs or alcohol, Silva said, the negative consequences can be the same - arrest, jail or potentially fatal traffic accidents.

The percentage of drivers killed in crashes on California roads who test positive for drugs has been on the rise, according to the Office of Traffic Safety. In 2010, 30 percent of those killed drivers tested positive for legal or illegal drugs.

Survey results came from 1,300 drivers in nine cities who agreed to give breath and saliva samples between 10 p.m. and 3 a.m. on Friday and Saturday nights. Breath samples were tested for alcohol, while the saliva was tested for marijuana and a number of other drugs, legal and illegal.

Marijuana use was at 7.4 percent, slightly above the percentage of people testing positive for alcohol. Of the 7.3 percent of people testing positive for alcohol, 23 percent also tested positive for at least one other drug, a combination that could increase the effect of both substances.

Collecting information has helped in efforts to fight drunken driving, and it can do the same for drugged driving, officials said.

"We want people to know that it's not just alcohol; it's legal, illegal and over-the-counter drugs that can impair people," Cochran said.